1. Field of the Invention
The invention relates to a method for selective separation of mixed synthetic organic materials, such as filled or unfilled, flameproof or non-flameproof, admixed or non-admixed polymers and/or copolymers that are waste materials to be recycled for upgrading, which synthetic organic materials can result from the destruction by grinding of automobiles and durable consumer goods that have reached the end of their serviceable lives, which selective separation method acts by separating these materials with regard to a density threshold selected in a dense medium consisting of fluid separating liquid suspensions, composed of powdery particles dispersed in an aqueous phase, wherein said suspensions are dynamically stabilised at the density threshold value selected for causing the selective separation of a predetermined fraction from the mixture of the used materials to be separated.
2. Description of Related Art
The used synthetic organic materials concerned generally come from the residues produced by grinding of automobiles and durable consumer goods that have reached the end of their serviceable life, in which many types of synthetic organic materials, such as filled or unfilled, flameproof or non-flameproof, admixed or non-admixed polymers and/or copolymers should be considered to be capable of being upgraded and in which many other materials are considered to be harmful contaminants, such as metals, minerals and other various contaminants that must first be removed. Other wastes, such as mixed industrial waste containing synthetic organic materials and packaging wastes such as polymers and/or copolymers from municipal collections and also containing mixed polymer materials can also be considered to be potentially upgradeable.
In industries for recycling used synthetic organic materials to be upgraded, various methods are used to separate stream constituents, substantially toxic and substantially contaminated, with a substantial content of upgradeable synthetic organic materials that must be separated from the pollutants, concentrated and sorted into homogenous streams of types of synthetic organic materials present, such as, for example, polyethylene, polypropylene, polystyrene (PS), acrylonitrile-butadiene-styrene copolymer (ABS), polyamides (PA), polyvinyl chloride (PVC), polyesters, polyurethane, polycarbonate, acrylic or metacrylic copolymers or the like, and all polymers capable of being filled, admixed, flameproofed or not.
These known methods currently make it possible to extract and separate streams to be treated, consisting of mixtures of synthetic organic materials to be upgraded and contaminants to be eliminated, which streams include:                a synthetic organic material phase having a density of less than 1,        a synthetic organic material phase having a density equal to or greater than 1,        a synthetic organic material phase, consisting, for example, of foams of polyethylene, polyurethane, waste from films, wires and the like,        a contaminant phase to be eliminated of which the constituents cannot be upgraded using such separation and upgrading methods, for example, sand, glass debris, wood debris, metal scraps and the like.        
One of these methods for separating polymer materials of all types from the grinding of automobiles and/or other end-of-life objects (described in the European patent EP 0918606 B), consists, after a grinding step causing the fragmentation of synthetic organic materials, preferably of performing mechanical separation by shape factor, followed by a first density separation step that causes the separation of all of the synthetic organic materials to be upgraded into two streams:                one having a density of less than 1, including in particular, and for example, unfilled polyolefins, such as polyethylenes (d=0.92 to 0.95), polypropylenes (around 0.9), ethylene and vinyl acetate copolymers, ethylene-propylene rubber copolymers (EPR), ethylene-propyene-diene-monomer copolymers (EPDM), polyethylene foams (PE), polypropylene (PP), polyurethane (PU) and the like,        the other having a density greater than or equal to 1, including, and for example:        polystyrene: unfilled PS (around 1.05)        acrylonitrile-butadiene-styrene copolymers: unfilled ABS (around 1.07)        polyvinyl chlorides: rigid unfilled PVC (around 1.30 to 1.40) and filled (around 1.40 to 1.55), plasticized such as plastisol and PVC foams        polycarbonates: unfilled PC, having a density d=1.20 to 1.24, PC filled with 20% glass fibres having a density d=1.3 or PC filled with 30% glass fibres having a density d=1.44        thermoplastic rubbers, except for alveolate thermosetting rubbers        polyurethanes: filled PU (d=around 1.21)        Talc-filled polypropylenes (Talc PP filled with between 5% and 40% talc)        filled polyethylenes: (PE filled with between 2% and 40% fillers)        unsaturated polyesters (ranging from around 1.10 to 1.13)        saturated polyesters (d≧1.20), filled or not (often filled with glass fibres)        polyamides: PA6 (d=1.13), PA6.6 (d=1.14), PA6.10 (d=1.08), PA11 (d=1.04), PA12 (d=1.02), filled or unfilled        polymethyl methacrylates: PMMA (d=1.18)        others.        
These two streams are subsequently treated so as to extract each component therefrom, separate them into homogeneous streams and treat them to make formulated pellets that can be used directly in plastic processing.
Although the stream of the upgradeable synthetic organic material mixture having a density of less than 1 is efficiently treated with a series of separation steps in an aqueous medium, in baths having a suitable density allowing for a fine selection of the various polymer compounds present in said flow, the same does not apply to the stream of the organic material mixture having a density greater than or equal to 1 of which the various synthetic organic materials are difficult to separate.
Indeed, for this second stream, which consists of a polymer mixture and/or filled or unfilled copolymers, of which the densities range from 1 to around 1.6, the separation of the various synthetic organic materials present in the mixture is performed by density in hydraulic separators of which the liquid separation medium consists of water, surfactants, and mineral compounds such as clay and in particular bentonite and optionally water-soluble compounds such as mineral salts, compounds implemented in order to increase the density of the liquid phase and bring it to a density value in principle enabling various synthetic organic materials to be separated into two distinct phases, one a supernatant and the other settled at the base of the separator, each phase forming a new stream, which is in turn subjected to another density separation process.
However, it appears that, during use, in particular in density separation facilities, used in industrial assemblies for processing used synthetic organic materials to be upgraded, the liquid separation media are not stable enough to allow for thorough selective density separations, i.e. providing highly homogenous separations into sorted material types, wherein the flows coming from the separation can be mixtures of a plurality of materials of which the respective densities are very similar to one another.
Indeed, a variety of particularly adverse phenomena occurring in this liquid density separation media have been observed; these adverse phenomena, which are real disadvantages, include:                a change in the rheology of said liquid media, which is manifested by a disturbing variation in their viscosity toward a more fluid or pasty state,        a deviation or a variation in the apparent density of the liquid media, which density cannot remain stable at the threshold level initially selected for good separation of the used synthetic organic materials to be upgraded, wherein the deviation (variation) causes a change in the composition of the flows separated by a dense liquid medium,        settling over time of some of the mineral compounds dispersed in the aqueous medium for creating the selected density, partially causing the change in the density of the liquid separation medium,        the near impossibility of finely separating the used synthetic organic materials to be upgraded, filled or not, when the density separation of the materials from one another must be performed on a density difference Δ=|0.001|, i.e. in an interval around the selected density “ds” of “ds±0.005”.        
Therefore, there is a certain significant problem with regard to the very fine density separation of used synthetic materials to be upgraded such as filled or unfilled polymers and/or copolymers that are used wastes to be recycled, from the destruction by grinding of automobiles and durable consumer goods that have reached the end of their serviceable lives, so as to obtain homogenous streams of separated materials, without any deviation in the density and mixture of the selected materials.
Optimizing the separation of solid materials that are difficult to separate from one another, having a density of at least 1 and generally much higher, in a dense liquid medium, is the subject of numerous research and industrial application studies.
The dense liquid medium of the prior art, generally having a density greater than 1, consists of an aqueous phase in which:                soluble mineral salts can be dissolved so as to increase the real density of the aqueous phase to a desired density value,        powder clays can be dispersed so as to create a suspension having an apparent density until the desired density is reached,        the two aforementioned means can be combined, that is, the solubilisation of salts increasing the density of the aqueous phase and the dispersion of clays in the aqueous phase at an increased density, so as to increase, insofar as possible, the stability of the suspension of clays in the densified aqueous phase.        
In the case of ore processing, for example, the density methods used consist of separating the ore from their matrix, after a mechanical action of grinding with the liberation mesh, in an aqueous suspension of dispersed powder clay, which clay acts as a densifying agent, at the appropriate concentration to enable the components to be separated into two phases, one supernatant and the other settling.
However, at the clay concentrations used to prepare the densified separation suspensions, the stability of said suspensions is entirely relative because the clay concentrations can change over time, according to the in the composition of the matrix to be eliminated of which the density is not stable and varies according to the extraction zone as well as the density of the ore to be extracted.
In these methods, the density threshold selected for the separation is relatively coarse and normally cannot reach the first decimal digit in separation sensitivity, i.e. for example, a densified separation medium with an apparent density between 1.4 and 1.5.
In the case of used synthetic organic materials to be upgraded, for example, such as fragmented polymer materials to be separated from one another or to be separated from their pollutants, dense liquid media separation methods are carried out, using the solubilisation of mineral salts in the aqueous phase or the dispersion of powder clays in an adequate amount to establish the threshold density for the division in the presence of surfactants.
Some documents have described such dense liquid separation media. A first document (DE 19964175) describes a technology enabling a heterogeneous mixture of fragmented polymers to be separated, according to their apparent density, in an aqueous saline solution constituting the dense liquid medium having a predetermined density, wherein the separation takes place in a laminar flow requiring the optimization of the flow conditions of the aqueous saline solution and the mixture of polymer materials to be separated.
The method thus described appears to be suitable only for a single density value, as it appears to be difficult to change the density of the dense liquid medium according to a wide range of values, this change being associated with the fact that, to reach relatively high densities, it is necessary to use increasingly high concentrations of solubilised salts; this method can therefore have an unacceptable production cost for separating used synthetic organic materials to be upgraded, with a very low added value, and all the more so as the technology used is subjected to an obvious corrosive action due to the liquid saline medium.
Another document (U.S. Pat. No. 3,857,489) describes a method for separating a stream of materials to be separated in a dense aqueous medium consisting of a powder clay suspension, dispersed in water, with an improved stability due to the addition of a water-soluble heteropolysaccharide-type clay-stabilizing agent (surfactant) to the suspension. However, the stability of the separating suspension is not adequately achieved, a phenomenon in which the clay particles settle, causing a significant variation in the density threshold chosen for the selective separation.
Another document (EP 0918 606 B1), as mentioned above, describes a method for separating fragmented polymer materials, from the grinding of automobile vehicles and/or other objects at the end of their serviceable lives, on a flow consisting of a mixture of filled or unfilled polymer and/or copolymers, of which the densities range from 1 to 1.6, wherein the separation in a dense liquid medium uses a suspension made of powder clay dispersed in water, so as to obtain a medium separating by density at a chosen density threshold. However, as described above, such a separating suspension has disadvantages that are difficult to overcome such as a variation in the rheology, the density over time, settling of the powder clay and an inability to set a particularly fine density threshold, for example, at the second decimal digit and to maintain it there.
Another document (U.S. Pat. No. 6,335,376 B1) describes a method for separating polymers present in a mixture of various polymers containing no metals or pollutants to be removed such as glass, foam, wood or the like. The method claimed consists of heating the mixture of these various polymers after a size selection, so as to cause the bubbling of at least one of the polymers of said mixture to be separated and to separate it from said mixture by means of a change in the apparent density of said polymer, caused by the heating.
This change in the apparent density causes a differentiation between at least one of the polymers of the heated mixture and the other polymers of the mixture, and a selective separation by a series of steps in which the density of each polymer is altered.
Therefore, this method uses specific separation means implementing heating means that set off a change in the structure causing the polymer materials to be separated.
Another document, the article KUNSTSTOFFBERATER, KUNSTSTOFF VERLAG describes a plant specifically intended for the production of PVC sheets, so that the inlet stream contains 95 to 100% PVC-H and PCV-P and 0 to 5% impurity, including a grinder, a washer, and density separators. This method comprises two successive density separation steps performed in a hydrocyclone at a flow of 200 m3/h, using a dense liquid medium which is an aqueous suspension of barium sulphate enabling the density of the water to be increased and the densities set as the separation threshold to be reached (d=1.2 and d=1.5).
However, this plant does not cause the separation of PVC-H (d=1.34 to 1.43) and PVC-P (d=1.20 to 1.35) from one another because the chosen separation density thresholds are such that they encompass the density values of PVC-H and PVC-P. Therefore, only the separation of the mixture of PVC-H and PVC-P with impurities occurs. Moreover, this plant does not allow for a particularly fine separation, because in the first separation at a density d=1.2, the products having a density of less than 1.2, such as polyolefins and wood, are supernatant. Products having a density greater than 1.2, which settle, constitute a mixture formed by PVC-H and PVC-P and impurities, which undergoes the second density separation at d=1.5. During this second separation step, the products having a density greater than 1.5, such as metals, glass and sand, settle and the mixture of PVC-H and PVC-P and probably some impurities having a density of between 1.2 and 1.5 is supernatant and recovered.
Thus, the prior art proposes various methods for separating materials to be separated, such as those resulting from the grinding of vehicles and/or durable consumer goods at the end of their serviceable lives, such as electrical household appliances, electronic equipment and the like which, after the recovery of metals, are synthetic organic materials, by implementing dense liquid media, with all of the disadvantages mentioned above.
However, the prior art does not propose methods for a particularly fine separation of various types of constituents, having a density equal to at least 1 and generally much higher than 1, forming a mixture of used synthetic organic materials to be upgraded, in a fragmented form.